INNER FOCUS OPTICAL SYSTEM

PROBLEM TO BE SOLVED: To provide an inner focus optical system which employs an inner focusing system suitable for an autofocus camera, has a small image height change rate when finely vibrating (wobbling) focus lens groups in a direction along an optical axis, is bright with an F number equivalent to 1.4, and has an angle of view of equivalent to 24 mm at conversion focal length of a 35 mm format.SOLUTION: An optical system comprises, in order from an object side to an image side, a first lens group G1 of negative refractive power, an aperture diaphragm, a second lens group G2 of positive refractive power, a third lens group G3 of negative refractive power, and a fourth lens group G4 of positive refractive power. When focusing from an object side infinity to an object side at a short distance, the third lens group G3 is moved toward an image plane side.SELECTED DRAWING: Figure 1 【課題】オートフォーカスカメラに適したインナーフォーカス方式を採用し、またフォーカスレンズ群を光軸に沿う方向へ微少振動（ウオブリング）させた際の像高変化率が小さく、F値が１．４と明るく、３５ｍｍ判換算焦点距離で２４ｍｍ相当の画角を有するインナーフォーカス光学系を提供する。【解決手段】物体側から像側へ順に、負の屈折力の第１レンズ群Ｇ１と、開口絞りと、正の屈折力の第２レンズ群Ｇ２と、負の屈折力の第３レンズ群Ｇ３と、正の屈折力の第４レンズ群Ｇ４とからなり、無限遠物体側から近距離物体側へのフォーカシングをする際、第３レンズ群Ｇ３が像面方向へ移動するインナーフォーカス光学系とする。【選択図】図１